The present invention relates to a toroidal type continuously variable transmission provided with a rotary element at a toroidal clearance defined between an input disc and an output disc such that torque is transmitted between the discs via the rotary element.
As disclosed in Published Japanese Translation of PCT International Publication for Japanese Patent Application No. 6(1994)-502476, the toroidal continuously variable transmission of this type is arranged such that grouped rotary elements of variable orientation transmit traction between matching part-toroidal type races formed on the confronting faces of coaxial and contra-rotating input and output discs. The input disc and output disc include center holes through which an input shaft, connected to a prime mover, extends. The input disc is connected with the input shaft in a manner to rotate in unison, whereas the output disc is rotatably carried on the input shaft.
A rotary velocity transmitted from the input disc to the output disc is varied with change of the orientation of the rotary elements. Specifically, when the rotary elements contact the input disc at a relatively high radius and the output disc at a relatively low one, the output disc rotates faster than the input disc and a variator is set at a high gear ratio.
When, on the other hand, the rotary elements contact the input disc at a relatively low radius and the output disc at a relatively high one, the output disc rotates slower than the input disc and the variator is set to a low gear ratio.
The rotary element is normally rotatably supported by a carriage extended orthogonally to a rotary shaft of the rotary element, an axis of the carriage is inclined at a predetermined caster angle relative to a plane including a torus center circle.
The input disc and output disc are urged by a hydraulic cylinder along a direction to come closer to each other, whereas the rotary element is also urged against the races of the discs by a hydraulic cylinder via the carriage supporting the same. Oil pressures generated by these hydraulic cylinders are controlled so that a force may be applied to the rotary element via the carriage for balancing the torque received by the rotary element. Thus, the roller angle is changed to strike a balance between the torque of the output disc and that of the input disc, thereby to maintain an appropriate torque ratio.
In practice, the roller receives a specific torque load according to any one of combinations of various essential parameters (e.g., requirement of an operator, engine load, engine velocity, final output velocity and the like). Therefore, a control system is designed to receive input representative of all the essential parameters and to set up within the hydraulic cylinder an appropriate oil pressure to match a reaction torque received by the roller in order to maintain an appropriate torque ratio between the input disc and the output disc.
On the other hand, a lubricant is directly jetted onto a rolling surface at a periphery of the rotary element for lubricant supply thereby allowing the rotary element to roll smoothly on the race.
In the prior art, the velocity of the rotary element is not sensed so that there has been provided no measure against the fear of abnormal behavior of the rotary element. This is because the sensing of the rotary velocities of the input disc and output disc permits the determination of a speed change ratio but not the determination of how much the rotary element slips on the discs. If, for example, the rotary element keeps working at an increased slip ratio, frictional heat will be generated to heat the rotary element as well as to evaporate the lubricant on the races, thus resulting in an abnormality such as flaking of the races. Furthermore, the oil between contact surfaces of the rotary element and the disc is heated to decrease traction and hence, a lowered transmissibility of the transmission results.
In order to meet a demand for the greatest possible reduction of size and weight of the toroidal type continuously variable transmission for use in vehicles, the discs and rollers must be downsized, as well.
However, if a required torque is to be transmitted under such conditions, contact pressure between the disc and the rotary element is increased. Particularly, when decreased in surface area as a result of the compact design, the rotary element is lowered in heat releasability. Hence, the temperature of the rotary element will rise to accelerate the deterioration of the lubricant. This leads to a fear of producing race flaking.
It is an object of the invention to provide a toroidal type continuously variable transmission designed to prevent the heat-up of the rotary element as well as to achieve the improvement of transmissibility and the reduction of size and weight.
For achieving the above objects, a preferred embodiment of the invention comprises a pair of discs in opposed relation; a rotary element disposed in a toroidal clearance defined between the discs for transmission of torque between the disc pair; and means for sensing the velocity of the rotary element.
The embodiment permits the monitoring of an actual velocity of the rotary element, thus contributing to the prevention of occurrence of abnormal behavior thereby avoiding the heat-up of the rotary element. As a result, the reduction of size and weight can be implemented in the toroidal type continuously variable transmission.
More preferably, the embodiment may further comprises a means for sensing the velocity of the disc and a signal output means for outputting a signal based on results given by the means for sensing the velocity of the rotary element and the means for sensing the velocity of the disc. The greatest factor for the heat-up of the rotary element is slippage of the rotary element against the disc. The slippage also affects traction at a contact portion between the rotary element and the disc. The embodiment enables the acquisition of information on the slippage of the rotary element and hence, the heat-up of the rotary element may be prevented more positively. Furthermore, the information on the slippage of the rotary element may be used to provide an optimal control of the traction at the contact portion between the rotary element and the disc so that the transmission may be improved in transmissibility.
It is preferred that the rotary element is formed with a plurality of raised/depressed portions on a side face thereof. In this case, the raised/depressed portions contribute to the increased surface area of the rotary element such that the rotary element may be improved in heat releasability for prevention of the heat-up thereof. This eliminates the fear of producing the race flaking due to the deterioration of the lubricant even if the rotary element and discs are downsized. Thus, the raised/depressed portions practically contribute to the reduction of size and weight of the continuously variable transmission. The raised/depressed portions may include at least one type of projections, recesses and through holes. It is particularly preferred that the raised/depressed portions are arranged with equal spacing and along a circumference about a rotary axis of the rotary element.